Probiotics are live microbial food ingredients that have a scientifically documented beneficial effect on human health. Probiotics are also used in animal feedstuffs either to improve animal health or productivity. They are used in pet foods, mainly to decrease unpleasant odours and improve consistency of fecal material.
Most of the dominant global strains of commercial probiotic bacteria belong to the bifidobacteria and the lactobacilli. However, bacteria from other genera are used in some parts of the world. For example, China uses a number of other genera, including Bacillus and a Clostridium. Enterococcus faecium has also been used worldwide, however, this genus is implicated in transfer of antibiotic resistance. In the Western world, both bifidobacteria and lactobacilli have a strong track record as safe and acceptable genera to use as probiotics. Other examples are discussed in:    Mogensen, G., Salminen, S., O'Brien, J., Ouwehand, A., Holzapfel, W., Shortt, C., Fonden, R., Miller, G D., Donohue, D., Playne, M., Crittenden, R., Bianchi-Salvadori, B. and R. Zink (2002). Food microorganisms—health benefits, safety evaluation and strains with documented history of use in foods Internat, Dairy Federation Bulletin No: 377: 4-9 and Mogensen, G., Salminen, S., O'Brien, J., Ouwehand, A., Holzapfel, W., Shortt, C., Fonden, R., Miller, G D., Donohue, D., Playne, M., Crittenden, R., Bianchi-Salvadori, B. and R. Zink (2002) Inventory of microorganisms with a documented history of use in food Internat, Dairy Federation Bulletin No: 377: 10-19.
It has been widely recognized by researchers and medical investigators that most health effects are conferred by a specific strain, and mostly not by the species in general. While many research groups have selected strains for useful probiotic properties for manufacture, for incorporation into foods, for survival in the gut, and for health properties, there is a dearth of information on performance in humans published in peer-reviewed journals.
Evidence is increasing that a probiotic food should contain selected strains of both lactobacilli and bifidobacteria. The concept is that the probiotic lactobacilli are useful in the young (where the gut microflora of infants is already naturally rich in bifidobacteria), and that addition of probiotic bifidobacteria becomes more important in the elderly. The numbers of indigenous bifidobacteria decline with aging if probiotics are not used. Bifidobacteria provide some protection against pathogens which are not able to be done effectively by lactobacilli alone. Adequate viable numbers of the strain of probiotic bacteria in the appropriate segment of the gut are essential if they are to be effective in an health sense. Most authorities consider 10 million bacteria per gram of food an appropriate dietary dose. Technically, this can be quite readily achieved. However, dose response curves have not been produced for any probiotic strain against any health condition.
Losses of bacterial numbers occur during manufacture, freeze drying and during shelf life. However, further losses occur during transit through the gastro-intestinal tract. The probiotic cultures will encounter gastric juices in the stomach ranging from pH 1.2 (on an empty stomach) through to pH 5.0. The cultures will be present in the stomach from around 40 minutes up to 5 hours. They will also encounter in the stomach and the small intestine, bile salts, lipolytic, hydrolytic and proteolytic enzymes, which are also able to kill bacteria. It is not until the probiotic bacteria reach higher pH regions of the gastro-intestine that they are able to grow or survive. Such regions are the ileum and the bowel. During this transit, the bacteria also have to compete with resident bacteria for space and for nutrients. They also have to avoid being flushed out of the tract by normal peristaltic action, and they have to avoid being killed by anti-microbials produced by other organisms. The bacteria have their most favourable growing conditions in the first third of the large bowel (the proximal bowel).
Ability to adhere to surfaces, such as intestinal mucosal layer, and the epithelial cell walls of the gut are thus important characteristics for a probiotic. The term “colonisation” is used, and means that the bacteria has mechanisms which enable it to survive in a region of the gastro-intestine on an on-going basis. It is generally believed that the microflora of the gastro-intestine are relatively stable in adults, and are not easily altered by changes in the conditions in the gut ecosystem.
Exceptions to this are administration of antibiotics, but even then the gut flora usually re-establish after sometime with a similar species composition.
Mechanisms of Action of probiotic bacteria include:                competitive exclusion (occupation of niches in the gut mucosal surface to prevent colonisation by infective species)        production of acid conditions (lactic acid fermentation by the bacteria leading to lowered gut pH)        effects on immune-mediated response        reduction of putrefactive and genotoxic intestinal reactions (leading to lower pre-carcinogen levels)        release of anti-microbials, such as bacteriocins        
Many diarrhoeal diseases originate from dysfunction in the small intestine, yet probiotic bacteria are not usually found in high numbers in that region, with the exception of some lactobacilli. There is little direct evidence available from healthy humans on microbial composition of the small intestine region. However, the effectiveness of probiotic bacteria in reducing diarrhoeal disease is quite well established. They are either functioning in transit through the small intestine, or acting through an immune effect. Most immune reactions will occur in the mucosal walls of the small intestine and not the large bowel, thus, if immune-modulation is believed to be the mechanism of action, then the probiotic must be present in the small intestine. The other region of diarrhoeal disturbance is the large bowel. Probiotic bacteria can establish in that region quite easily.
In addition to diarrhoeal disorders, probiotic bacteria are effective in lessening lactose intolerance, provided bacteria are chosen which have high beta galactosidase enzyme function. Lactose intolerance effects manifest in the bowel. There are a large number of other emerging health claims made for probiotics. These centre particularly around the bowel eg., bowel cancer, irritable bowel syndrome and inflammatory bowel diseases (such as Crohn's disease). Accordingly, release of probiotic lactobacilli in the last half of the small intestine is preferred. Release of bifidobacteria is usually aimed to occur in the large bowel. Greater immune responses tend to occur with bifidobacteria than with lactobacilli, thus, there is an argument that bifidobacteria in the small intestinal regions are of great importance.
Daily consumption of the probiotic is necessary if the target site is in the small intestine, as it is unlikely that the bacteria can adhere to the gut wall in sufficient numbers (except perhaps some lactobacilli). However, daily consumption may not be necessary if the target site is the large bowel, as growth of the bacteria and colonisation may occur.
Probiotic bacteria with good characteristics for effectiveness against disease and other conditions may not have good survival characteristics (eg resistance to low pH, bile salts, proteolytic and hydrolytic enzymes, resistance to antibiotics, adherence to cell walls). Protection of the bacteria during transit to the target site is usually necessary.
Protection may be achieved in several ways: encapsulation in a slow release pharmaceutical compound; encapsulation in a gum or in alginate; encapsulation in a resistant starch or in inulin in combination with a gum; protection by incorporation in a food containing resistant starch; or in a dairy food where the proteins and fats may provide some protection.
U.S. Pat. No. 5,422,121 discloses a coating incorporating a film forming polymer having hydrophilic groups and a polysaccharide decomposable in the colon which is useful in delivering dosages to the colon.
U.S. Pat. No. 5,840,860 discloses the delivery of short chain fatty acids to the colon by covalently linking them to a carbohydrate carrier.
U.S. Pat. No. 6,060,050 discloses a combination of a probiotic bacteria such as bifidobacterium with high amylose starch as a carrier which also acts as a growth or maintenance medium in the large bowel or other regions of the gastrointestinal tract.
U.S. patent application 20030096002 discloses a matrix for use in the controlled release of microorganisms. The matrix is formed of a hydrophobic wax and a release modifying agent selected from polysaccharides, starch, an algae derivative or a polymer.
U.S. Pat. No. 6,413,494 discloses a colonic drug delivery vehicle consisting of a polysaccharide such as pectin.
Some probiotics need protection during processing as well as during delivery to the gastro intestinal tract. They may be water or oxygen sensitive and need protection to maintain viability during processing storage and transporting. European patent 1213347 discloses a method of drying and preserving yeasts and microorganisms by mixing them with a matrix material that absorbs water
It is an object of this invention to provide a means of encapsulating probiotics to protect them from deterioration during processing and storage and enable them to be delivered to specific sites in the gastrointestinal tract.